Cellular telephones, pagers, hand held games, portable radios, tape recorders, compact disk players, "boom" boxes, two-way mobile radios, laptop and portable computers, portable power tools, golf carts, electric vehicles, and powered wheelchairs all have at least one thing in common: they all use batteries. When getting ready to leave the home or office with one of these devices the user will ask himself one or more of the following questions: When did I last charge the battery? How much have I used it since then? Is there enough charge in the battery to last through my meeting or flight or trip? What is the state of my backup battery? When did I last charge it?
These questions go unanswered as batteries do not provide an indication of their present capacity. Some devices attempt to estimate the remaining charge by measuring the current drawn from the battery and the time that it is drawn. However, this method does not account for the natural discharge of the battery or the fact that an older battery may not be able to charge to 100% of its rated capacity.
Therefore, there is a need for a user to be able to quickly determine the present and potential capacity of a battery so that the user can make a decision as to whether to recharge the battery, or to bring a spare battery, or to install another battery.